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Abstract:

Time for which an ejection port surface of a print head has been exposed
to the exterior since the end of the last cleaning operation is predicted
and accumulated as an accumulated exposure time. A cleaning timing is set
to be a timing when the accumulated exposure time coincides with a set
time set according to the ambient temperature and humidity of an area in
which a label printer is installed. In principle, a cleaning operation is
performed at the cleaning timing. However, when the cleaning timing comes
during the current consecutive printing operation, the cleaning operation
is not performed during the current consecutive printing operation but at
a time before the start of the current consecutive printing operation or
a time after the end of the current consecutive printing operation.

Claims:

1. An ink jet printing method of using a print head capable of ejecting
ink through an ejection port formed on an ejection port surface to form
an image on a print medium and performing a cleaning operation for
removing a substance hindering ejection of the ink, at a preset cleaning
timing,wherein when the cleaning timing comes during a consecutive
printing operation of consecutively printing images, the cleaning
operation is not performed during the consecutive printing operation but
before start of the consecutive printing operation or after end of the
consecutive printing operation.

2. The ink jet printing method according to claim 1, wherein the cleaning
timing is set on the basis of an accumulated dot count, andthe
accumulated dot count is an accumulated number obtained by predicting and
accumulating number of times that the print head ejects ink between end
of the last cleaning operation and end of the current consecutive
printing operation.

3. The ink jet printing method according to claim 1, wherein the cleaning
timing is set on the basis of an accumulated exposure time, andthe
accumulated exposure time is an accumulated time obtained by predicting
and accumulating time for which the ejection port surface of the print
head is exposed to an exterior between end of the last cleaning operation
and end of the current consecutive printing operation.

4. The ink jet printing method according to claim 3, wherein the cleaning
timing is a timing when the accumulated exposure time reaches a time set
on the basis of ambient temperature and humidity of the print head.

5. The ink jet printing method according to claim 1, wherein the cleaning
timing includes a first cleaning timing set on the basis of an
accumulated dot count and a second cleaning time set on the basis of an
accumulated exposure time,the accumulated dot count is an accumulated
number obtained by predicting and accumulating number of times that the
print head ejects ink between end of the last cleaning operation and end
of the current consecutive printing operation,the accumulated exposure
time is an accumulated time obtained by predicting and accumulating time
for which the ejection port surface of the print head is exposed to the
exterior between end of the last cleaning operation and end of the
current consecutive printing operation,when the first cleaning timing is
predicted to come during the current consecutive printing operation, the
cleaning operation is performed before start of the current consecutive
printing operation, andwhen the first cleaning timing is predicted not to
come during the current consecutive printing operation and the second
cleaning timing is predicted to come during the current consecutive
printing operation, the cleaning operation is performed before the start
of the current consecutive printing operation.

6. The ink jet printing method according to claim 5, wherein when the
first cleaning timing is predicted to come during the current consecutive
printing operation even though the cleaning operation is performed before
the start of the current consecutive printing operation, the current
consecutive printing operation is not performed.

7. The ink jet printing method according to claim 5, wherein when the
second cleaning timing is predicted to come during the current
consecutive printing operation even though the cleaning operation is
performed before the start of the current consecutive printing operation,
the current consecutive printing operation is not performed.

8. The ink jet printing method according to claim 5, wherein the cleaning
operation performed at the first cleaning timing exerts a stronger
recovery force than the cleaning operation performed at the second
cleaning timing, the recovery force being required to recover an ink
ejection state of the print head.

9. The ink jet printing method according to claim 5, wherein the
accumulated dot count is predicted on the basis of data required to
perform the consecutive printing operation.

10. The ink jet printing method according to claim 5, wherein the
accumulated exposure time is predicted on the basis of data required to
perform the consecutive printing operation.

11. An ink jet printing apparatus using a print head capable of ejecting
ink through an ejection port formed on an ejection port surface to form
an image on a print medium, the ink jet printing apparatus having
cleaning means capable of performing a cleaning operation for removing a
substance hindering ejection of the ink, at a preset cleaning timing, the
apparatus comprising:cleaning timing storage unit that stores the
cleaning timing;instructing unit that instructs the cleaning means to
perform the cleaning operation when the cleaning timing comes;first
storage unit that storages an accumulated dot count that is an
accumulated number obtained by predicting and accumulating number of
times that the print head ejects ink between end of the last cleaning
operation and end of the current consecutive printing operation;first
determining unit that determines whether or not the cleaning timing set
on the basis of the accumulated dot count comes during the current
consecutive printing operation; andcontrol unit that controls, when the
first determining unit determines that the cleaning timing comes during
the current consecutive printing operation, the instructing unit so that
the cleaning operation is not performed during the current consecutive
printing operation but before start of the current consecutive printing
operation or after end of the current consecutive printing operation.

12. The ink jet printing apparatus according to claim 11, further
comprising:second storage unit that stores an accumulated exposure time
that is an accumulated time obtained by predicting and accumulating time
for which the ejection port surface of the print head is exposed to an
exterior between end of the last cleaning operation and end of the
current consecutive printing operation;second determining unit that
determines whether or not the cleaning timing set on the basis of the
accumulated exposure time comes during the current consecutive printing
operation; andcontrol unit that controls, when at least one of the first
and second determining units determines that the cleaning timing comes
during the current consecutive printing operation, the instructing unit
so that the cleaning operation is not performed during the current
consecutive printing operation but before start of the current
consecutive printing operation or after end of the current consecutive
printing operation.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an ink jet printing method and an
ink jet printing apparatus which print an image on a print medium while
performing a cleaning operation for removing a substance (thickened ink
or dirt) hindering ejection of ink, at a preset timing.

[0003]2. Description of the Related Art

[0004]Printing apparatuses (ink jet printing apparatuses) are widely used
which print images by ejecting ink to print media such as print sheets.
To eject ink, the ink jet printing apparatus uses a print head having a
plurality of nozzles and ink ejection ports (outlets of the nozzles)
formed therein. The plurality of ink ejection ports (hereinafter referred
to as "ejection ports") are formed on an almost flat ejection port
forming surface (hereinafter referred to as an "ejection port surface")
of the print head. Two types of print heads are available; one of these
types of print head ejects ink while moving in a main scanning direction
together with a carriage, and the other type of print head (line head
type) ejects ink while fixed and stopped. The former type of print head
is used for ink jet printing apparatus based on what is called a serial
scan scheme. The other type of print head is used for what is called full
line type ink jet printing apparatuses.

[0005]With these printing apparatus, if thickened ink or dirt (the
substance hindering ink ejection) is collected around the nozzles or
ejection ports in the print head during an image printing operation or
standby (non-printing operation), the ink may be inappropriately ejected
or printed images may be degraded. As a technique for solving this
problem, a cleaning technique is known such as pressurization recovery,
wiping, or preliminary ejection (idle ejection). The pressurization
recovery is a process of pressurizing the interior of the print head to
push the thickened ink, bubbles, dirt, or the like out of the nozzles.
The wiping is a process of wiping the ejection port surface using a
cleaning blade (cleaning member) made up of an elastic body. The
preliminary ejection (idle ejection) is a process of ejecting ink from
the print head in order to remove the thickened ink or dirt instead of
printing images.

[0006]For the cleaning operation, the image printing operation must be
temporarily suspended. Japanese Patent Laid-Open No. 2005-349841
describes a technique of performing a cleaning operation during the
non-printing operation to reduce delay resulting from the cleaning
operation. Furthermore, Japanese Patent Laid-Open No. 2004-358791
describes a technique of periodically performing the cleaning operation
on the basis of instructions from a host computer to reduce the time for
which the printing operation is suspended owing to the cleaning
operation.

[0007]However, with a large printing volume (the amount of printing during
a consecutive printing operation of consecutively printing images), even
though the cleaning operation is performed before the consecutive
printing operation, the cleaning operation may need to be performed again
during the consecutive printing operation. In this case, the
above-described conventional techniques cannot reduce the suspension time
for the printing operation. That is, the cleaning operation is performed
during the consecutive printing operation. The cleaning operation is
started at the timing (cleaning timing) when a predetermined condition is
met. The condition is often set on the basis of the total amount of ink
ejected from the print head, a change in the condition of the print head,
or the like. Therefore, the printing apparatus automatically starts the
cleaning operation when the condition is met. Thus, the printing
operation is suspended at a user's unintended timing, and the cleaning
operation is started.

[0008]An ink jet printing apparatus (commonly called a label printer) is
known which consecutively prints images on a plurality of labels
temporarily attached to a band-like card board so as to be arranged in a
longitudinal direction. The label printer may be used to print images on
the labels in synchronism with an external instrument. A label attaching
operation may be performed during a post-process after the printing
operation of the label printer has been completed. Thus, if the printing
operation is suspended at the user's unintended timing as described
above, the label printer may fail to synchronize with the external
instrument or the post-process operation may be complicated.

[0009]Furthermore, one type of label printer has a function of allowing
the user to pre-instruct the printer on a unit for batch printing (the
unit for consecutive printing of images on a plurality of labels) (see,
for example, Japanese Patent Laid-Open No. 62-182029 (1987)). This type
of label printer is effective in printing images of the same content on a
plurality of labels. If the labels have different print contents, when
the printing operation is suspended at the user's unintended timing as
described above and instead the cleaning operation is performed, the
above-described problems, that is, the failure to synchronize with the
external instrument and the complicated post-process operation, become
more serious.

[0010]Furthermore, a full line type ink jet printing apparatus having a
plurality of the line head type print heads arranged in a print medium
conveying direction has a long distance between a print head located on
the most upstream side of the print medium conveying direction and a
print head located on the most downstream side of the print medium
conveying direction. Thus, for example, a print medium positioned below
the print head on the conveying direction most upstream side may be
different from a print medium positioned below the print head on the
conveying direction most downstream side (the succeeding print medium and
the preceding print medium). To suspend the printing operation for the
cleaning operation, it is necessary to complete printing the print medium
on which the image is being printed (preceding print medium), then
discharge the preceding print medium, and move the succeeding print
medium to a downstream position in the conveying direction where the
succeeding print medium does not hinder the cleaning operation, before
performing the cleaning operation. Consequently, when the printing
operation is restarted after the cleaning operation has been completed,
the print medium on which the corresponding image has not been completely
printed yet is moved to the position where image printing is possible.
This requires a process of conveying the succeeding print medium in a
direction opposite to the conveying direction (back feed). This may in
turn further degrade productivity, prevent the printing apparatus from
synchronizing with the external instrument, or complicate the
post-process operation.

SUMMARY OF THE INVENTION

[0011]The present invention provides an ink jet printing method and an ink
jet printing apparatus which prevent a consecutive printing operation of
consecutively printing images from being suspended by a cleaning
operation.

[0012]In the first aspect of the present invention, there is provided an
ink jet printing method of using a print head capable of ejecting ink
through an ejection port formed on an ejection port surface to form an
image on a print medium and performing a cleaning operation for removing
a substance hindering ejection of the ink, at a preset cleaning timing,
wherein when the cleaning timing comes during a consecutive printing
operation of consecutively printing images, the cleaning operation is not
performed during the consecutive printing operation but before start of
the consecutive printing operation or after end of the consecutive
printing operation.

[0013]In the second aspect of the present invention, there is an ink jet
printing apparatus using a print head capable of ejecting ink through an
ejection port formed on an ejection port surface to form an image on a
print medium, the ink jet printing apparatus having cleaning means
capable of performing a cleaning operation for removing a substance
hindering ejection of the ink, at a preset cleaning timing, the apparatus
comprising: cleaning timing storage means for storing the cleaning
timing; instructing means for instructing the cleaning means to perform
the cleaning operation when the cleaning timing comes; first storage
means for storing an accumulated dot count that is an accumulated number
obtained by predicting and accumulating number of times that the print
head ejects ink between end of the last cleaning operation and end of the
current consecutive printing operation; first determining means for
determining whether or not the cleaning timing set on the basis of the
accumulated dot count comes during the current consecutive printing
operation; and control means for, when the first determining means
determines that the cleaning timing comes during the current consecutive
printing operation, controlling the instructing unit so that the cleaning
operation is not performed during the current consecutive printing
operation but before start of the current consecutive printing operation
or after end of the current consecutive printing operation.

[0014]According to the present invention, the cleaning operation is not
performed during the consecutive printing operation of consecutively
printing images but before the start of the consecutive printing
operation or after the end of the consecutive printing operation. This
prevents the consecutive printing operation from being suspended. This in
turn makes it possible to avoid failing to synchronize with an external
instrument or complicating a post-process operation, improving
productivity (printing efficiency). Furthermore, by performing the
cleaning operation before the start of the consecutive printing
operation, it is possible to maintain the high quality of printed images
obtained by the consecutive printing operation.

[0015]Further features of the present invention will become apparent from
the following description of exemplary embodiments (with reference to the
attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a diagram illustrating a system configuration in which a
host computer is connected to a label printer as an example of the
present invention;

[0017]FIG. 2 is a front view schematically showing the general
configuration of the label printer in FIG. 1;

[0018]FIG. 3 is a block diagram showing an electrical system in the label
printer in FIG. 2:

[0019]FIG. 4 is a plan view showing a part of continuous label paper;

[0020]FIG. 5 is a diagram illustrating an example of cleaning timings set
on the basis of an environment in which the label printer is used;

[0021]FIG. 6 is a diagram illustrating an example of cleaning timings set
on the basis of the number of times (ejection dot count) that ink
droplets are ejected from a print head;

[0022]FIG. 7 is a diagram illustrating a set time varied depending on
temperature and humidity; and

[0023]FIG. 8 is a flowchart showing an example of an ink jet based image
forming method according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0024]An embodiment of the present invention will be described below with
reference to the drawings. An ink jet printing apparatus in the
embodiment described below is an example in which the present invention
is applied to a label printer capable of consecutively printing images on
a plurality of labels temporarily attached to a band-like card board so
as to be arranged in a longitudinal direction (consecutive printing
operation).

[0025]With reference to FIGS. 1 and 2, description will be given of the
general configuration of the label printer as an example of the present
invention.

[0026]FIG. 1 is a diagram illustrating a system configuration in which a
host computer is connected to the label printer as an example of the
present invention. FIG. 2 is a front view schematically showing the
general configuration of the label printer in FIG. 1.

[0027]A label printer 10 is connected, by a cable 14, to a host computer
(host apparatus) as an information processing apparatus. The host
computer 12 outputs image data, sheet size information, consecutively
printed sheet count information (information indicating the number of
labels on which images are consecutively printed), and the like to the
label printer 10 via the cable 14 as control commands. The host computer
12 receives status information (variation information such as error
information) on the label printer 10 as a control command to notify the
user of the status of the label printer 10.

[0028]Reference numeral 20 denotes a continuous label sheet (an example of
a print medium) composed of a band-like card board to which a plurality
of labels are temporarily attached along a longitudinal direction of the
card board. The label printer 20 can consecutively print images on the
plurality of labels temporarily attached to the continuous label sheet 20
(a consecutive printing operation). The number of labels on which the
images are consecutively printed can be appropriately set by the user.
The continuous label sheet 20 is installed in a roll unit 22. The
continuous label sheet 20 is supplied to a conveying section comprising a
conveying motor 32 and a conveying belt 34 and then conveyed in the
direction of arrow A.

[0029]The label printer 10 has a print head 40K for ejecting black (K)
ink, a print head 40C for ejecting cyan (C) ink, a print head 40M for
ejecting magenta (M) ink, and a print head 40Y for ejecting yellow (Y)
ink. The print heads 40K, 40C, 40M, and 40Y are full line type print
heads each having a nozzle row of a length corresponding to the width of
the labels temporarily attached to the continuous label sheet 20. The
nozzle row is a row in which a plurality of nozzles capable of ejecting
the ink are arranged. The nozzles eject ink through ejection ports formed
on substantially flat ejection port surfaces 44K, 44C, 44M, and 44Y of
the print heads. Electrothermal transducers (heaters), piezo elements, or
the like may be used as ejection energy generating elements that eject
the ink. The electrothermal transducers can bubble ink in the nozzles and
utilize the resulting bubbling energy to eject the ink through the
ejection ports. The four print heads 40K, 40C, 40M, and 40Y eject the
black ink, cyan ink, magenta ink, and yellow ink, respectively, to allow
full color images to be printed on the labels. The label printer 10
consecutively prints images on the labels the number of which is
specified by the host computer 12.

[0030]The inks ejected from the print heads 40K, 40C, 40M, and 40Y are fed
from ink cartridges 42K, 42C, 42M, and 42Y corresponding to the
respective ink colors, by means of a pump (not shown).

[0031]The roll unit 22 comprises a roll driving shaft 24 around which the
continuous label sheet 20 is installed, a roll sensor lever 26 the
position of which is varied by the slack of the continuous label sheet
20, and a sheet feeding motor 79 (see FIG. 3) that drives the roll
driving shaft 24. The continuous label sheet 20 is stably fed by
controllably driving and stopping the sheet feeding motor 79 (see FIG. 3)
depending on the position of the roll sensor lever 26.

[0032]The label printer 10 comprises a cleaning unit 50 that removes
thickened ink or dirt from the ejection port surfaces 44K, 44C, 44M, and
44Y of the print heads 40K, 40C, 40M, and 40Y. The cleaning unit 50
comprises a wipe blade that wipes the ejection port surfaces 44K, 44C,
44M, and 44Y to wipe off the thickened ink or dirt attached to the
ejection port surfaces 44K, 44C, 44M, and 44Y, and a tub that receives
the inks ejected from the print heads 40K, 40C, 40M, and 40Y by a
preliminary ejection operation. Four cleaning units 50K, 50C, 50M, and
50Y are arranged in association with the print heads 40K, 40C, 40M, and
40Y. Moreover, two extra cleaning units are provided. The cleaning units
50K, 50C, 50M, 50Y, and the like (hereinafter also collectively referred
to as the "cleaning unit 50") have the positions thereof controlled by a
cleaning unit control motor 74 (see FIG. 3) to perform a print head
cleaning operation and a capping operation as described below.

[0033]An electrical system in the label printer 10 will be described with
reference to FIG. 3.

[0034]FIG. 3 is a block diagram showing the electrical system in the label
printer in FIG. 2.

[0035]The host computer 12 transfers image data for printing or the like
to the label printer 10 as a control command to instruct the label
printer 10 to start a printing process. The host computer 12 can send a
sheet setting command that specifies the number of labels to be printed
by the label printer 10, the type and size of the continuous label sheet
20, and the like, a command that specifies a print speed, and a command
for the consecutively printed sheet count information (information
indicating the number of labels on which images are consecutively
printed).

[0036]The label printer 10 uses a communication driver 62 to control
communications to receive the commands (the data command, the sheet
setting command, and the like) from the host computer 12. The image data
received by the label printer 10 is expanded and drawn on RAMs 46K, 46C,
46M, and 46Y in bit map form as the image data for respective color
components. On the RAMs 46K, 46C, 46M, and 46Y, the image data for the
color components corresponding to the black (K), cyan (C), magenta (M),
and yellow (Y) inks are expanded in bit map form. Furthermore, the sheet
setting command specifying the number and size of labels and the number
of labels to be printed is stored in the RAM 64R. The data command and
the sheet setting command, and the like are expanded on the RAMs 46K,
46C, 46M, and 46Y, the print heads 40K, 40C, 40M, and 40Y are moved to a
print position by a head mechanism control motor 66.

[0037]To print images on a plurality of labels, a main controller 68
sequentially reads, from the RAMs 46K to 46Y, the corresponding color
image data in synchronism with the conveyance of the continuous label
sheet 20. The image data is output, via a head driving circuit 70, to the
print heads 40K to 40Y, which eject the corresponding color inks. The
print heads 40K to 40Y eject the corresponding color inks on the basis of
the input image data to print multicolor images on the labels. The main
controller 68 acts as cleaning instructing means, first determining
means, second determining means, and control means according to the
present invention. As described below, the instructing means instructs
the printer to perform the cleaning operation. The first determining
means determines whether or not a cleaning timing set on the basis of an
accumulated dot count is reached during the consecutive printing
operation. The second determining means determines whether or not a
cleaning timing set on the basis of an exposure accumulated time is
reached during the consecutive printing operation. The control means
controls the instructing means on the basis of the determination of the
first and/or second determining means.

[0038]When image printing based on a plurality of image data is completed
or a predetermined time has elapsed, that timing (time) is stored in a
nonvolatile RAM 72. The number of times that the ink is ejected from the
print heads 40K to 40Y as droplets is accumulated for each of the print
heads 40K to 40Y and stored in the RAM 64R. Since the ink ejected as
droplets forms ink dots on the label, the number of times that the print
heads 40K to 40Y ejects the ink corresponds to the number of dots formed.
The number of times that the print heads 40K to 40Y ejects the ink is
hereinafter referred to as the dot count. The accumulated dot count for
each of the print heads 40K to 40Y is hereinafter referred to as the
accumulated dot count. As described below, it is possible to predict, on
the basis of the image data, the accumulated dot count for each of the
print heads 40K to 40Y between the end of the last cleaning operation and
the end of the current consecutive printing operation. The predicted
accumulated dot count is stored in the RAM 64R. Thus, the RAM 64R is an
example of storage means for the accumulated dot count according to the
present invention (first storage means). When the cleaning operation is
started, the stored accumulated dot count is cleared to zero. When the
cleaning operation is completed, the counting is restarted.

[0039]The following time is also accumulated as an accumulated exposure
time: the time for which the print heads 40K to 40Y are located at
positions where the print heads 40K to 40Y are not capped by the tub of
the cleaning unit 50, that is, the exposure time for which the ejection
port surfaces of the print heads 40K to 40Y are exposed to the air. In
this case, the exposure time from the end of the last cleaning operation
until the end of the current consecutive printing operation is
accumulated as the accumulated exposure time. The exposure time can be
predicted on the basis of data required to perform the current continuous
printing operation as described below. The RAM 64 also stores the
accumulated exposure time. Consequently, the RAM 64R has a function of
storing the accumulated exposure time (second storage means) according to
the present invention. When the cleaning operation is started, the stored
accumulated exposure time is cleared to zero. When the cleaning operation
is completed, the counting is restarted.

[0040]To perform the cleaning operation, the cleaning unit control motor
74 moves the cleaning unit 50 (see FIG. 2) and allows the wipe blade to
wipe the ejection port surfaces of the print heads. To perform, as the
cleaning operation, the preliminary ejection operation for ejecting ink
not contributing to image printing (idle ejection), from the print head,
the cleaning unit control motor 74 moves the cleaning unit 50 so that the
tub of the cleaning unit 50 can receive the ink ejected by the
preliminary ejection operation. Furthermore, the following data is input
to the main controller 68 via an IO port 76: measurement data from a
temperature sensor and a humidity sensor (neither of the sensors are
shown) which measure the ambient temperature and ambient humidity of the
print heads 40K to 40Y, and detection data from a position detecting
sensor and the like provided in mechanical sections of the label printer.
The above-described control in the label printer is performed by the main
controller 68 by executing control programs stored in a ROM 78. The ROM
78 is an example of cleaning timing storage means according to the
present invention and stores an exposure time table shown in FIG. 7
described below.

[0041]The continuous label sheet 20 will be described with reference to
FIG. 4.

[0042]FIG. 4 is a plan view showing a part of the continuous label sheet.

[0043]The continuous label sheet 20 is elongate and is wound, like a roll,
around a cylindrical core having a hollow portion. A plurality of
piece-like labels 20b each with a printable surface are tacked to a card
board 20a for the continuous label sheet 20 at equal intervals. The label
printer 10 can consecutively print different images on the respective
labels 20b at a high speed (consecutive printing operation) by
superimposing, on the plurality of labels, common form data and field
data varying with the label. In the present example, the form data is
data for frame lines 20c, and the field data is data for character
strings 20d and a barcode 20e.

[0044]With reference to FIGS. 5, 6, and 7, description will be given of a
cleaning timing for performing the cleaning operation and how to change
the cleaning timing. The cleaning operation removes a substance hindering
ink ejection (thickened ink or dirt), from the print heads 40K to 40Y.
Examples of the cleaning operation include the wiping and preliminary
ejection, described above and pressurization recovery, described below. A
cleaning timing is preset as timing for performing the cleaning
operation.

[0045]FIG. 5 is a diagram illustrating an example of cleaning timings set
on the basis of an environment in which the label printer is used. FIG. 6
is a diagram illustrating an example of cleaning timings set on the basis
of the number of times that the ink has been ejected from the print heads
40K to 40Y (dot count). FIG. 7 is a diagram illustrating a set time Ta
set on the basis of temperature and humidity.

[0046]Two conditions for regularly performing the cleaning operation are
set for the label printer 10. The contents (type) of the cleaning
operation performed vary between the two conditions.

[0047]The first condition specifies that the accumulated time for which
the ejection port surfaces of the print heads remain uncapped
(accumulated exposure time) reach a preset value (set time) Ta. In
principle, when the accumulated exposure time reaches the set value Ta,
the cleaning operation is performed. However, the cleaning operation may
not be performed as described below. The cleaning operation performed in
this case is the preliminary ejection. This cleaning operation is
hereinafter referred to as cleaning A for convenience. Even if no ink has
been ejected through one of the nozzles until the set time Ta, the
preliminary ejection ejects thickened ink present near the ejection port
surface for that nozzle, that is, the ink with increased viscosity owing
to the evaporation of moisture to the air. The appropriate ink ejection
condition can thus be maintained.

[0048]The second condition specifies that the accumulated number of times
that the ink has been ejected from the print head (accumulated dot count)
reach a preset dot count (set count) Nb. In principle, when the
accumulated dot count reaches the set count Nb, the cleaning operation is
performed. However, the cleaning operation may not be performed as
described below. The cleaning operation in this case is such that the
pressurization recovery, the wiping, and the preliminary ejection are
performed in this order. This cleaning operation is hereinafter referred
to as cleaning B for convenience. The pressurization recovery is a
process of pressurizing the ink in the print head to forcibly discharge
the ink into the tub of the cleaning unit 50 through the nozzle. The
cleaning B is a cleaning operation more powerful than the cleaning A.
That is, since the thickened ink and dirt are pushed out and wiped off by
the pressurization recovery operation and the wiping operation and the
preliminary ejection operation is further performed, a strong recovery
force can be exerted.

[0049]First, with reference to FIGS. 5 and 7, description will be given of
a cleaning timing for performing the cleaning A.

[0050]As shown in FIG. 7, the set time Ta is varied depending on the
ambient temperature and humidity of the area in which the label printer
10 is installed (the ambient temperature and humidity of this area are
the same as those of the print head). For example, when the temperature
is at most 5° C. and the humidity exceeds 75%, the set time Ta is
100 seconds. When the temperature exceeds 25° C. and the humidity
is at most 25%, the set time Ta is 80 seconds. When the accumulated
exposure time reaches the set time Ta, the first condition is met and the
cleaning A is in principle performed. The table shown in FIG. 7 is stored
in the ROM 78. The temperature and humidity are measured by the
above-described temperature sensor and humidity sensor (neither of the
sensors are shown) and input to the main controller 68 via the IO port
76. The main controller 68 reads the table shown in FIG. 7 from the ROM
78 to select the set time Ta.

[0051]The label printer 10 prints images on every consecutive printing
number of labels; the consecutive printing number is specified by the
host computer 12 (see FIG. 3). The consecutive printing number refers to
the number of labels on which images are consecutively printed
(consecutive printing). Reference numerals Tp1, Tp2, Tp3, and Tp4 denote
the time required for the first, second, third, and fourth consecutive
printing operations, respectively. While the images are being printed on
the labels, the print heads 40K to 40Y are at print positions. Thus,
during the consecutive printing operation, the time for which the print
heads 40K to 40Y have been exposed to the air since a time T0 when the
last cleaning A was complete is sequentially accumulated. For example,
when the amounts of time Tp1, Tp2, Tp3, and Tp4 required for the
respective consecutive printing operations are the same, that is, the
amount of time Tp, the exposure time from the time T0 when the last
cleaning A is completed is accumulated every amount of time Tp. As
described below, the exposure time can be predicted on the basis of data
required to perform the consecutive printing operation. Even during the
consecutive printing operation, the exposure time is accumulated
according to the progress of the operation. When the first consecutive
printing operation (the duration of the first consecutive printing
operation is Tp2) is completed after the last cleaning A, the accumulated
exposure time is Tp1. Subsequently, when the second consecutive printing
operation (the duration of the consecutive printing operation is Tp2) is
completed, the accumulated exposure time is Tp1+Tp2. Subsequently, when
the third consecutive printing operation (the duration of the third
consecutive printing operation is Tp3) is completed, the accumulated
exposure time is Tp1+Tp2+Tp3.

[0052]When the third consecutive printing operation is completed, the
fourth consecutive printing operation (the duration of the fourth
consecutive printing operation is Tp4) is performed. In the present
example, the accumulated exposure time reaches the set time Ta during the
fourth consecutive printing operation. A timing TA when the accumulated
exposure time coincides with the set time Ta corresponds to the cleaning
timing. In principle, the cleaning A is performed at the timing TA.
However, if the cleaning A is performed during the fourth consecutive
printing operation, the printing operation is suspended. Thus, in the
present example, when the timing TA is expected to be coming when the
accumulated exposure time coincides with the set time Ta, the cleaning A
is not performed at the timing TA but at a time TA1 before the start of
the fourth consecutive printing operation or at a time TA2 after the end
of the fourth consecutive printing operation. As a result, the cleaning
operation is not performed during the consecutive printing operation
specified by the host computer 12. This eliminates the need to suspend
the printing operation or to feed the continuous label sheet backward.

[0053]Now, the second condition described above will be described.

[0054]The second condition specifies that the accumulated number of times
that the ink has been ejected from the print head (accumulated dot count)
reach the set count Nb as described above. When this condition is met,
the cleaning B is in principle performed. However, the cleaning B may not
be performed as described below.

[0055]The set count Nb is present in accordance with the characteristics
of the print heads 40K to 40Y. As described above, the label printer 10
prints images on every consecutive printing number of labels; the
consecutive printing number is specified by the host computer 12 (see
FIG. 3).

[0056]Reference numerals NP1, Np2, Np3, and Np4 in FIG. 6 each denote the
accumulated number of times (accumulated dot counts) that the ink has
been ejected from one of the print heads during the first, second, third,
and fourth consecutive printing operations, respectively. Np1, Np2, . . .
are sequentially added to the accumulated dot count every time one
consecutive printing operation is completed after a time T1 when the last
cleaning B is completed. The accumulated dot count can be predicted on
the basis of image data (one of the data required to perform the
consecutive printing operation). Thus, even during the consecutive
printing operation, the dot count is accumulated according to the
progress of the operation. When the first consecutive printing operation
(the ink ejection count during the first consecutive printing operation
is Np1) is completed after the last cleaning B, the accumulated dot count
is Np1. When the second consecutive printing operation (the ink ejection
count during the second consecutive printing operation is Np2) is
completed, the accumulated dot count is Np1+NP2. Subsequently, when the
third consecutive printing operation (the ink ejection count during the
third consecutive printing operation is Np3) is completed, the
accumulated dot count is Np1+NP2+Np3.

[0057]When the third consecutive printing operation is completed, the
fourth consecutive printing operation (the ink ejection count during the
fourth consecutive printing operation is Np4) is performed. In the
present example, the accumulated dot count reaches the set count Nb
during the fourth consecutive printing operation. A timing TB when the
accumulated dot count coincides with the set count Nb corresponds to the
cleaning timing. In principle, the cleaning B is performed at the timing
TB. However, if the cleaning B is performed during the fourth consecutive
printing operation, the printing operation is suspended. Thus, in the
present example, when the timing TB is predicted to be coming when the
accumulated dot count coincides with the set count Nb, the cleaning B is
not performed at the timing TB but at a time TB1 before the start of the
fourth consecutive printing operation or at a time TB2 after the end of
the fourth consecutive printing operation. As a result, the cleaning
operation is not performed during the consecutive printing operation
specified by the host computer 12. This eliminates the need to suspend
the printing operation or to feed the continuous label sheet backward.

[0058]Since the dot count depends on image data, the dot count value
during printing of a consecutive printing number of labels can be
predicted on the basis of received image data. Specifically, if the
specified consecutive printing number of labels is 10, the received image
data corresponds to three labels, and image data on the remaining seven
labels is to be received during the printing operation, the dot count
value corresponding to the image data on the 10 labels is predicted on
the basis of the received image data on the three labels. For example, if
the dot count value corresponding to the image data on the three labels
is 3,000 dots, the dot count value corresponding to the image data on the
10 labels can be predicted to be 10,000 dots. If the dot count value
varies significantly with the image data, the predicted dot count value
is multiplied by a coefficient. The prediction of the dot count value is
performed by the main controller 68, and the result of the prediction is
stored in the RAM 64R.

[0059]As described above, when the cleaning timing comes during the
consecutive printing operation of consecutively forming images, the
cleaning operation is not performed at that cleaning timing but before
the start of or after the end of that consecutive printing operation.
This prevents the consecutive printing operation from being suspended,
making it possible to avoid degrading productivity (reducing printing
efficiency), failing to synchronize with an external instrument, or
complicating post-process operations. Furthermore, if the cleaning
operation is performed before the start of the consecutive printing
operation, the quality of print images can be prevented from being
degraded.

[0060]With reference to FIG. 8, an example of an ink jet printing method
according to the present invention will be described.

[0061]FIG. 8 is a flowchart showing an example of the ink jet printing
method according to the present invention.

[0062]This flow is started when the host computer 12 (see FIG. 3)
transmits a start signal to the label printer 10 (see FIG. 3) to start
the current consecutive printing operation. The host computer 12
transmits image data and command data specifying a sheet size, a printing
speed, the consecutive printing number, and the like to the label printer
10, which receives the data for performing the consecutive printing
(S801). The main controller 68 (see FIG. 3) executes a predicting process
to predict the dot count value on the basis of the received image data.
That is, the total of the dot count value is predicted which is obtained
when the printing of the specified consecutive printing number of labels
is completed (S802). For example, the main controller 68 predicts, as the
dot count value, the total of the number of times that the ink is ejected
from the print head 40K during the current consecutive printing
operation. The label printer 10 continues to receive the subsequent print
data.

[0063]Before the current consecutive printing operation is started, the
dot count value predicted in S802 has been added to the accumulated dot
count stored in the RAM 64R, and the resulting value has been stored in
the RAM 64R as a new accumulated dot count. Subsequently, the main
controller 68 (see FIG. 3) compares the new accumulated dot count with
the set count Nb (S803). Upon determining that the accumulated dot count
is greater than the set count Nb, the main controller 68 proceeds to
S804. In S804, the main controller 68 compares the predicted dot count
value (the ink ejection count only during the current consecutive
printing operation) with the set count Nb. If the dot count value is
determined to be smaller than the set count Nb, the cleaning unit control
motor 74 (see FIG. 3) or the like is driven to perform the cleaning B
before the current consecutive printing operation is started (S805). At
this time, the cleaning timing corresponds to TB1 in FIG. 6. The cleaning
B maintains the print head in the appropriate ink ejection condition.
Furthermore, since the dot count value is smaller than the set count Nb,
the cleaning B is not performed during the current consecutive printing
operation.

[0064]After the cleaning B is performed in S805, the accumulated dot count
(the count value for the cleaning B) and the accumulated exposure time
(the count value for the cleaning A), described below, are cleared to
zero (S806); both the accumulated dot count and the accumulated exposure
time are stored in the RAM 64R. Subsequently, the current consecutive
printing operation is started (S813). The reason why not only the count
value for the cleaning B (accumulated dot count) but also the count value
for the cleaning A (accumulated exposure time) is cleared in S806 is that
the cleaning B is more powerful than the cleaning A and that performing
the cleaning B more reliably improves the ink ejection condition of the
print head.

[0065]When the main controller 68 determines in S804 that the predicted
dot count value (the ink ejection count only during the current
consecutive printing operation) is greater than the set count Nb, even if
the cleaning B is performed before the start of the current consecutive
printing operation, the cleaning timing TB comes again during the current
consecutive printing operation to suspend the consecutive printing
operation. Thus, upon determining in S804 that the predicted dot count
value is greater than the set count Nb, the main controller 68 causes the
label printer 10 to display an error (S814) and waits for the host
computer 12 to re-specify the consecutive printing number (S815). The
main controller 68 returns to the process of predicting the dot count
value on the basis of the re-specified consecutive printing number
(S802), and then executes the subsequent process.

[0066]Upon determining in S803 that the accumulated dot count is smaller
than the set count Nb, the main controller 68 shifts to a process of
checking the condition for the cleaning A (S807). In S807, on the basis
of the detected values of the temperature and humidity of the vicinity of
the label printer 10, the main controller 68 acquires a time Ta (stored
in the ROM 78) that is the condition for the cleaning A, from the
exposure time table in FIG. 7. Subsequently, the main controller 68
predicts the exposure time value of the print head expected to be
measured when until the current consecutive printing operation is
completed, on the basis of the printing number and printing speed
specified for the current consecutive printing operation (S808). The
specified printing number and printing speed are part of the data
required to perform the current consecutive printing operation.

[0067]The exposure time predicted in S808 is added to the accumulated
exposure time stored in the RAM 64R, before the current consecutive
printing operation is started. The resulting value is stored in the RAM
64R as a new accumulated exposure time. Subsequently, the main controller
68 compares the new accumulated exposure time with the set time Ta
(S809).

[0068]Upon determining in S809 that the new accumulated exposure time is
longer than the set time Ta, the main controller 68 proceeds to S810. In
S810, the main controller 68 compares the predicted exposure time (the
exposure time only during the current consecutive printing operation)
with the set time Ta. Upon determining that the exposure time is shorter
than the set time Ta, the main controller 68 performs the cleaning A
before the start of the current consecutive printing operation (S811).
The cleaning A maintains the print head in the appropriate ink ejection
condition. Furthermore, since the predicted exposure time is shorter than
the set time Ta, the cleaning A is not performed during the current
consecutive printing operation. After the cleaning A is performed in
S811, the accumulated exposure time (the count value for the cleaning A)
stored in the RAM 64R is cleared to zero (S812). Subsequently, the
current consecutive printing operation is started (S1813).

[0069]When the main controller 68 determines in S810 that the predicted
exposure time is longer than the set time Ta, even if the cleaning A is
performed before the start of the current consecutive printing operation,
the cleaning timing TA comes again during the current consecutive
printing operation to suspend the consecutive printing operation. Thus,
upon determining that the predicted exposure time is longer than the set
time Ta as described above, the main controller 68 causes the label
printer 10 to display an error (S814) and waits for the host computer 12
to re-specify the consecutive printing number (S815). The main controller
68 returns to the process of predicting the dot count value on the basis
of the re-specified consecutive printing number (S802).

Other Embodiments

[0070]In the above-described embodiment, the label printer 10 is connected
to the host computer 12. However, the label printer 10 may be connected
to an external instrument such as a labeling machine. In this case, the
consecutive printing number may be specified using communication
standards such as RS-232C as an I/F for the external instrument.
Alternatively, the unit for a printing operation specified by the host
computer 12 may be the distance of a printing range on print media or
printing time instead of the number of print media.

[0071]Furthermore, the present invention is widely applicable to various
ink jet printing apparatuses other than the label printer. For example,
the present invention is applicable to an ink jet printing apparatus
printing print media one by one and an ink jet printing apparatus
printing elongate print media every predetermined distance or every
predetermined amount of time. The printing apparatuses may be based on a
serial scan scheme or a full line scheme. Basically, any printing
apparatus may be used provided that the printing apparatus can
consecutively perform the printing operation a number of times using the
number of print media, the printing range, or the printing time as an
operation unit, as the consecutive printing operation.

[0072]Furthermore, the cleaning operation may be any of various operations
such as the wiping, preliminary ejection, and pressurization recovery,
described above, as well as suction recovery. The suction recovery is an
operation of introducing a negative pressure into a cap that caps the
ejection ports in the print head to suck and discharge the ink not
contributing to image printing, into the cap. The cleaning operation
essentially has only to remove the substance hindering the ink ejection
(thickened ink or dirt) from the print head.

[0073]Furthermore, the present invention may be applied to a system
composed of a plurality of instruments (for example, a host computer, an
interface instrument, and a printer) or to an apparatus made up of one
instrument (for example, a copier or a facsimile machine). Moreover, of
course, the functions of the above-described embodiment can be provided
by supplying a system or an apparatus with a storage medium in which a
software program code implementing the functions is stored, and allowing
a computer (or a CPU or MPU) in the system or apparatus to read and
execute the program code stored in the storage medium. In this case, the
program code itself read from the storage medium implements the functions
of the above-described embodiment. The storage medium storing the program
code constitutes the present invention. The storage medium for supplying
the program code may be, for example, a floppy (registered trade mark)
disk, a hard disk, an optical disk, a magneto optic disk, a CD-ROM, a
CD-R, a magnetic tape, a nonvolatile memory card, or a ROM.

[0074]Furthermore, the functions of the above-described embodiment may be
provided not only by allowing the computer to execute the read program
code but also by allowing an OS (Operating System) or the like operating
on the computer to execute a part or all of the actual process on the
basis of instructions in the program code. Of course, the present
invention includes the case where this process is used to provide the
functions of the above-described embodiment.

[0075]It is also possible to write the program code read from the storage
medium to a memory provided in an expansion board inserted into the
computer or in an expansion unit connected to the computer and then to
allow a CPU or the like provided in the expansion board or unit to
execute a part or all of the actual process on the basis of instructions
in the program code. Of course, the present invention includes the case
where this process is used to provide the functions of the
above-described embodiment.

[0076]While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0077]This application claims the benefit of Japanese Patent Application
No. 2007-053857, filed Mar. 5, 2007, which is hereby incorporated by
reference herein in its entirety.